Silicate Biomaterials for Orthopaedic and Dental Implants

Many developed nations including the U.S.A. have increasingly older populations as birth rates have declined and life expectancy has increased over the twentieth century. A corresponding factor of two increase in demand for artificial joint and dental implants is anticipated over the next thirty years (Piehler 2000). The development of biomaterials for orthopaedic and dental implants with improved properties and durability in the human body is critical to deal with this aging population. Broadly speaking, the first-generation of biomaterials was bioinert, whereas bioactive and bioresorbable materials represented improved, second-generation materials. Still, one third to one half of the prostheses fail within 10–25 years and require a second surgery (Shirtliff and Hench 2003 and references therein). The challenge facing the development of improved orthopaedic and dental biomaterials for the future is to design materials that are biocompatible, capable of bearing high stress and loads, and that invoke positive cellular and genetic responses for the rapid repair, modification, regeneration and maintenance of the affected tissue in the human body, i.e., tissue engineering. In this chapter, we will provide a brief history of the use of implants, and review the requirements that a biomaterial must fulfill to be used effectively as an orthopaedic or dental implant, the chemical composition-structure-activity of different types of silicate biomaterials including glasses and ceramics, the chemical reactions that occur at the silicate implant/solution interface involving inorganic ions and organic biomolecules (mainly proteins). We will also review studies that show the effects of different synthetic solutions, used experimentally to mimic human blood plasma, on in vitro tests of bioactivity. Our focus will be on dense silicate biomaterials that have up to ~20% porosity and high mechanical strength, in contrast to porous biomaterials with ~40–60% porosity and scaffold materials that have ~80% porosity and almost no mechanical strength. We will …